[Fwd: termios flow control]

[Joel Sherrill]

I am forwarding this to the list so others can attempt to
answer this. :)

Please cc everyone since I don't know if the person asking is
on the mailing list.

Thanks.

--joel

WuHao wrote:
>
> ------------------------------------------------------------------------
>
> Subject:
> termios flow control
> From:
> WuHao <derossi at mail.ustc.edu.cn>
> Date:
> Thu, 24 May 2007 17:30:05 +0800
> To:
> "rtems-users at rtems.com" <rtems-users at rtems.com>
>
> To:
> "rtems-users at rtems.com" <rtems-users at rtems.com>
>
>
> Hi:
> I am reading code of rtems 4.7.0.
> Here are 2 questions about termios flow control.
> Suppose input controlled with XON/XOFF protocol:
>
> 1.When the RawInbuf reaches highwater,a character indicate XOFF will be
> writen to device immediately if the RawOutBuf if idle or the output is
> not working,and a bit in flow control(FL_ISNTXOF) will be set indicate
> that the XOFF signal is already sent. However,the write action will
> cause a dequeue callback where the tty->t_dqlen will be added by 1.As a
> result, the "Tail" of the data buffer will not be correct.
>
> 2.Opposite to question XOFF,when the RawInbuf reaches lowwater,a
> character indicate XON will be writen to device immediately if the
> RawOutBuf if idle or the output is not working.Different to "highwater
> reaching",none of flow control bits is set to indicate that the XON
> signal is already
> sent.As a result,the following dequeue callback will detect that a XON
> signal is required to send but not send yet.Then a XON signal is sent
> again,reduce tty->t_dqlen by 1. This case will keep RowOutBuf's tail
> correct,but the XON signal is sent twice.
>
> Thanks a lot.
>
>
>